• 한국세라믹학회지
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• 제32권12호
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• pp.1392-1400
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• 1995

WC-10wt%Co-Al2O3 ceramic composites, using both the SHS (Self-propagating High Temperature Synthesis) synthesized WC powder method and commercial WC powder, were prepared by varing WC-Co/Al2O3 vol% ratio and sintering temperature (1350℃∼1650℃) for 1 hr in Ar atmosphere. Mechanical characterization has been investigated by Instron meterial testing system and Vicker's hardness test. Compositional and structural chracterizations were carried out by energy-dispersive analysis of X-ray (EDAX) data and scanning electron microscope (SEM). Electrical characterization was carried out by the electrical resistivity measurement using 4-point probe method. As sintering period increased and Al2O3 contents decreased in WC-10wt%Co-Al2O3 ceramic composite, shrinkage and relative density increased, resulting in maximum values at 1600℃. Also the major matrix phase changed with increasing Al2O3 content from 0 to 100 vol%. It was also identified by SEM, EDAX, and electrical resistivity measurement. Based on the results of analysis of flexural strength, toughness and hardness, the mechanical properties of WC-10wt%Co-Al2O3 ceramic composites using the SHS synthesized WC powder were better than those WC-10wt%Co-Al2O3 ceramic composites using commercial WC powder because WC-10wt%Co-Al2O3 ceramic composites using the SHS synthesized WC powder were sintered very well due to small initial particle size. By the addition of 40 vol% Al2O3 [60(WC=10wt%Co)-40Al2O3], it was possible to obtain a proper candidate as a superalloy.

• Journal of Electrochemical Science and Technology
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• 제14권4호
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• pp.377-387
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• 2023

Ni-W/Al₂O₃ nano-composites were electrodeposited on mild steel substrate for mechanical and corrosion resistance applications. This study focused on the preparation of Ni-W/Al₂O₃ nano-composite coating with various quantity of Al₂O₃ incorporations. The addition of Al₂O₃ in the electrolytes were varied from 1-10 g/L in electrolytes and the Al₂O₃ incorporation in Ni-W/Al₂O₃ nano-composite coatings were obtained from 1.82 to 13.86 wt.%. The incorporation of Al₂O₃ in Ni-W alloy matrix influenced the grain size, surface morphology and structural properties were observed. The distributions of Al₂O₃ particle in alloy matrix were confirmed using electron microscopy (FESEM and TEM) and EDAX mapping analysis. The crystal structure informations were studied using X-ray diffraction method and it confirms that the deposits having cubic crystal structure. The better corrosion rate (0.87 mpy) and microhardness (965 HV) properties were obtained for the Ni-W/Al₂O₃ nano-composite coating with 13.86 wt.% of Al₂O₃ incorporations.

• 한국수소및신에너지학회논문집
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• 제23권6호
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• pp.581-587
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• 2012

Thermal aging effect on NSR kinetics was studied over Pt/Co/Fe/Ba/$Al_2O_3$ catalyst. The amount of $NO_x$ uptake over Pt/Co/Fe/Ba/$Al_2O_3$ calcined at $400^{\circ}C$ increased with increasing NSR temperature from $200^{\circ}C$ to $400^{\circ}C$, where amount of $NO_x$ uptake is the highest at $400^{\circ}C$ with mol ratio of $NO_x$/Ba = 0.5. Thereafter, the amount of $NO_x$ uptake at $400^{\circ}C$ decreased with the higher calcination temperature, where Pt/Co/Fe/Ba/$Al_2O_3$ catalyst calcined at $700^{\circ}C$ showed an amount of $NO_x$ uptake with the mol ratio of $NO_x$/Ba=0.062. Result of XRD and NSR showed that Fe addition into Pt/Co/Fe/Ba/$Al_2O_3$ suppressed sintering of Pt crystallites and make $NO_x$ uptake larger, compared to no addition of Fe into Pt/Co/Fe/Ba/$Al_2O_3$ catalyst. From BET result, it was found that the change of specific surface area was relatively small by the thermal aging process. Therefore, it was found that the sintering of Pt crystallites caused the decrease of $NO_x$ uptake during NSR reaction and Fe played a role to suppress the sintering process of Pt crystallites caused by thermal aging.

• 한국결정성장학회지
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• 제2권2호
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• pp.71-76
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• 1992

$0.05Pb(Al_{2/3}W_{1/3})O_3-0.95Pb(Zr_{0.52}Ti0.48)O_3$를 기본 조성으로 $MnO_2,Fe_2O_3$를 첨가제로 하여 사진식각법(Photolithography)을 이용 세라믹 필터를 제작하였다. $MnO_2$의 첨가량이 증가함에 따라 전기 기계 결합 계수(Kp)가 낮아지며, $Fe_2O_3$의 경우 Kp값은 57% 정도로 우수하나 기계적 품질 계수(Qm)는 $MnO_2$첨가의 경우에 비해 상대적으로 낮은 값을 보여주고 있다. $MnO_2$0.3wt% 첨가의 경우 3dB 대역폭은 155kHz, $ Fe_2O_3$0.1wt%인 경우 260kHz로써 Qmr값이 크기에 반비례하였으며, 군지연시간 특성은 $MnO_2$의 경우 Gaussian 특성을,$Fe_2O_3$의 경우 Butterworth 특성을 나타내었다.

• Journal of Welding and Joining
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• 제14권6호
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• pp.109-118
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• 1996

Al$_2$O$_3$-TiO$_2$powders of six different compositions were plasma-sprayed on Ti substrate. The spray powders and the spray coated layers were analysed and compared using SEM and X-RD. The elastic properties (specific elastic constant and damping coefficient) of the coated specimens were measured in order to select the optimum composition range of ceramics for use in a speaker diaphragm. A correlation between the microstructure and elastic properties was also investigated. When $Al_2$O$_3$powders with 0- 13% TiO$_2$were plasma sprayed, the coated layers were composed of metastable y-Al$_2$O$_3$with small amount of $\alpha$-Al$_2$O$_3$and the content of $\alpha$-Al$_2$O$_3$was increased with TiO$_2$content. Specific elastic constant was rapidly increased with 2 and 13% TiO$_2$addition to $Al_2$O$_3$. The internal damping was nearly unchanged with TiO$_2$content The specific elastic constant seemed to be dependent on the content of $\alpha$-Al$_2$O$_3$in the coated layer.

• 공업화학
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• 제5권2호
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• pp.285-294
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• 1994

몇 종류의 담지 금촉매를 통상의 함침법과 공침법에 의하여 제조하였다. 금입자의 크기, 산소의 흡착량, CO와 NO의 흡착특성 그리고 산화환원 특성 등의 조사를 통하여, 금의 첨가효과와 활성점의 생성에 관해 연구하였다. 함침법에 의한 촉매의 금입자들은 30~100nm 정도로 크고 균일하지 않았으나, 공침법에 의한 촉매는 약 4nm인 초미립자의 상태로 매우 균일하게 분산되어 있었다 $Au/Al_2O_3$촉매에 있어서, 불활성인 $Al_2O_3$에 금의 첨가로 $N_2O$의 분해가 일어났으며, CO의 비가역흡착은 일어나지 않았으나, $O_2$는 원자상으로 비가역흡착하였다. 산소의 흡착점은 활성점이 금입자 표면에 존재하는 원자 전부가 아니라 반구형인 금입자와 담체의 경계면 주위에 한정된 활성점이었다. 저온의 $Al_2O_3$에서는 CO의 가역흡착과 비가역흡착이 일어났지만, 소량의 금의 첨가에 의하여 어느 쪽의 흡착도 약해졌다. $Au/Co_3O_4$촉매에서 CO에 대한 친화성은 $Co_3O_4$에 비해 크게 감소하였다. 환원과정에서는 금의 첨가효과가 보이지 않고, 재산화과정에서 금의 첨가효과가 뚜렷하게 나타나, 첨가된 금은 환원상태의 코발트의 재산화를 촉진시켰다.

• 한국세라믹학회지
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• 제32권7호
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• pp.846-852
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• 1995

The multiply reinforced mullite-zirconia composites were prepared with addition of Al2O3 particles, platelets, and fibers. The sinter-HIP specimens (presintered at 1$700^{\circ}C$ and hipped at 1$600^{\circ}C$) showed that the fracture toughness of Al2O3 fiber reinforcement (4.4 MPa.{{{{ SQRT {m} }}) was higher than those of platelet (4.0 MPa.{{{{ SQRT {m} }}) and of particle (3.9MPa.{{{{ SQRT {m} }}) reinforcement, whereas the fracture strength of Al2O3 particle reinforcement (304 MPa) was higher than those of platelet (293MPa) and of fiber (248MPa) reinforcement.

• 한국세라믹학회지
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• 제33권10호
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• pp.1138-1146
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• 1996

Al2TiO5 powder was prepared by the sol-gel processing from th metal alkoxides ; aluminium sec-butoxide (Al(OC4H9)3 and tetraethyl orthotitanate (Ti(OC2H5)4) The particles of Al2TiO5 produced from alkoxides were measured to be below $1.5mutextrm{m}$ and mre than 90% weere below 1 ${\mu}{\textrm}{m}$ however those from commercial alumina and titania were over 0.5-7${\mu}{\textrm}{m}$ and only 60% were below 1${\mu}{\textrm}{m}$ and 90% were below 2.5${\mu}{\textrm}{m}$ Therefore Al2TiO5 powder produced from alkoxides had the narrower distributionin size than that produced from the commercial alumina and titania powders. The addition of mullite or Al2O3 powder to the prepared aluminum titanate inhibited the grain growth and this resulted in decreased and increase in density.

• 한국세라믹학회지
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• 제27권4호
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• pp.457-464
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• 1990

This paper presents the influence of the loading rate on the room temperature fracture toughness of a brittle Al2O3 and a SiC whisker reinforced Al2O3 composite. Dynamic fracture toughness tests were conduced using compressive fatigue pre-cracked notched round bars loaded in tension to produce a stress intensity rate K1=106 MPa√m/sec. The experimental results show that for each loading rate the fracture toughness values obtained for the ceramic matrix composite are higher than the corresponding values for the single phase alumina. In addition, both the reinforced and unreinforced ceramic are singnificantly tougher under dynamic loading than static loading. This dynamic and quasi-static fracture initiation behaviro can be interpreted by identifying quantitatively the mode of fractuer initiation as a function of loading rate.

• 한국수소및신에너지학회논문집
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• 제26권5호
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• pp.423-430
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• 2015

$Cu/ZnO/Al_2O_3$ catalysts for water gas shift (WGS) reaction were synthesized by co-precipitation method with the fixed molar ratio of Cu/Zn/Al precursors as 45/45/10. Copper and zinc precursor were added into sodium carbonate solution for precipitation and aged for 24h. During the aging period, aluminum precursor was added into the aging solution with different time gap from the precipitation starting point: 6h, 12h, and 18h. The resulting catalysts were characterized with SEM, XRD, BET surface measurement, $N_2O$ chemisorption, TPR, and $NH_3$-TPD analysis. The catalytic activity tests were carried out at a GHSV of $27,986h^{-1}$ and a temperature range of 200 to $400^{\circ}C$. The catalyst morphology and crystalline structures were not affected by aluminum precursor addition time. The Cu dispersion degree, surface area, and pore diameter depended on the aging time of Cu-Zn precipitate without the presence of $Al_2O_3$ precursor. Also, the interaction between the active substance and $Al_2O_3$ became more stronger as aging duration, with Al precursor presented in the solution, increased. Therefore, it was confirmed that aluminum precursor addition time affected the catalytic characteristics and their catalytic activities.